This invention relates to variable inductance lamp ballast apparatus and, more particularly, to such a ballast apparatus which can be manufactured in a very accurate, simple and inexpensive fashion.
In U.S. Pat. No. 3,873,910, dated Mar. 25, 1975, to Willis is disclosed a ballast control device having variable inductance for use with HID lamps which comprises a main winding and a control winding positioned on opposite sides of an added, gapped shunt. When the control winding is closed, such as by means of a triac, the inductance of the device is decreased in order to control the average power delivered to the HID lamp.
U.S. Pat. No. 4,037,148, dated July 19, 1977, to Owens et al discloses a circuit for sensing a lamp operating condition to actuate a triac control such as used in the aforementioned U.S. Pat. No. 3,873,910.
U.S. Pat. No. 3,886,405, dated May 17, 1945, to Kubo discloses a large variety of different techniques for sensing the operating condition of an HID lamp in order to generate a control signal.
In U.S. Pat. No. 3,590,316, dated June 29, 1971, to Engel et al is disclosed an electronic wattmeter which can be used to generate a signal in order to control the wattage delivered to an HID lamp.